OVERALL PROJECT SUMMARY/ABSTRACT The goal of our program is to elucidate the molecular mechanisms of HCMV regulation of host signaling in the establishment and maintenance of viral latency and reactivation, and determine how viral dysregulation of CD34+ Hematopoietic Progenitor Cells (HPCs) signaling may compromise hematopoiesis. HCMV remains a significant cause of morbidity and mortality after Solid Organ Transplantation (SOT) and Hematopoietic Stem Cell Transplantation (HSCT), and myelosuppression is a common clinical manifestation of HCMV infection in these patients. HPCs represent a critical reservoir of latent HCMV in the transplant recipient, thereby providing a source of virus for dissemination to visceral organs. Preliminary data from our group using an in vitro CD34+ HPC model and mice engrafted with human fetal bone marrow, liver and thymus (huBLT mice) have shown that HCMV regulation of Epidermal Growth Factor Receptor (EGFR) and downstream signaling in CD34+ HPCs is essential for viral latency and reactivation as well as hematopoiesis. Our group has shown that multiple HCMV genes expressed in latently infected CD34+ HPCs including the UL133-138 locus, US28, UL7 and HCMV miRNAs target multiple signaling pathways activated by EGFR to control viral latency/reactivation and hematopoiesis. We hypothesize that HCMV fine tunes the activity of EGFR and its downstream pathways to balance states of viral latency and reactivation. We also hypothesize that HCMV fine tunes signaling and cytokine secretion to impact hematopoiesis. Further, we propose that this regulation meets antagonistic needs to promote dissemination but limit broad hematopoietic differentiation to control reactivation. This program project will test each of these hypotheses using the in vitro CD34+ HPC model in combination with the huBLT mouse model and samples from SOT and HSCT patients. The complexity of signaling events and approaches to comprehensively address questions on viral latency and hematopoiesis can only be achieved through a collaborative effort under a PPG mechanism. Therefore we propose five highly integrated research projects (Project 1: UL133/8 regulation of host cell signaling in viral latency and hematopoiesis; Project 2: HCMV miRNA regulation of host cell signaling in viral latency and hematopoiesis; Project 3: HCMV US28 regulation of host cell signaling in viral latency and hematopoiesis; Project 4: HCMV UL7 regulation of host cell signaling in viral latency and hematopoiesis; Project 5: HCMV regulation of host cell signaling and cytokines in myelosuppression), two scientific cores (Humanized Mouse Core; Genomics, Biostatistics and Bioinformatics Core) to service these projects, and an Administrative Core to oversee and coordinate the entire program.